Present day four-stroke internal combustion (IC) engines employ a solid piston moving to and fro inside a cylindrical bore, to perform the four operations, viz., (i) suction, (ii) compression, (iii) power and (iv) exhaust. The present day two-stroke IC engines do the first three of the above four operations by solid piston only, the only difference being in that the crankcase side of the piston is used for an intake or suction operation, so that while the solid piston is doing compression on one side it is doing suction on the other side.
The fourth operation, viz., the exhaust, done in present-day 2-stroke IC engines, may be viewed with interest to compare with the present invention in the sense that two dissimilar gases in direct contact result in filling the closed chamber with gaseous medium. Though the above exhaust process may also be called as partial gaseous piston method, the present invention differs fundamentally in the method and purpose, the details and the novelty of which have been given below.
More generally, present-day reciprocating air-compressors employ a solid piston moving inside a cylindrical bore to perform suction and compression alternatively. However, a solid piston reciprocating in a closed chamber presents various problems of cost and inefficiency. Bore and piston have to be precisely machined and sealing rings are necessary for effective sealing, and loss of power due to friction is high because of the sliding piston. A heavy lubrication system is required for the sliding piston, and a heavy cooling system is necessary because the piston will seize if the equipment runs at elevated temperatures. Because of the heavy cooling system, loss of heat energy in cooling water or air is high. Wear and tear of bore and piston necessitates frequent maintenance or replacement of parts like the sleeve, piston rings, etc. Vibration (due to unbalanced reciprocating mass) and noise are high.
Limitations of existing solid-piston IC engines also are known. Because the stroke and the clearance volume are fixed, the compression ratio of the engine is fixed. In other words, the suction and compression pressures are almost fixed for a given speed of the engine. Because of the above points, an engine designed for a specific fuel, e.g. gasoline, cannot be easily altered for other fuels like diesel or LPG (Liquid Petroleum Gas).
The power of a solid-piston IC engine is dependent on the speed to a great extent. In fact, while the actual requirement in most of the applications is high-torque at low speed and lower-torque at high speed, the IC engine delivers power the other way. Moreover, the engine is capable of delivering power only within a specified range of RPM; there is an idling speed and a maximum speed. It cannot deliver power at zero RPM like a steam engine. In order to be ready for delivering power, the engine has to run at idling speed, wasting fuel.
The solid-piston engine gives acceptable performance (both fuel economy-wise as well as torque capacity-wise) only within a narrow bandwidth of the engine speed. This fact necessitates accessories like a clutch and gear system to obtain the same power at low as well as high output speeds, at the wheels of the vehicle. Moreover, the engine starting apparatus is heavy and quite costly due to high frictional torque and the high idling speed. The ignition timing, the rate of combustion, and the velocity and position of pistons must be coordinated failing which, problems like pre-ignition, knocking, etc., arise.